Room-by-Room Sizing: The Key to Improving Heat Pump Retrofits

Cooling isn’t just about comfort anymore, it’s about health and safety.

Wildfires, smoky air, and extreme heat are becoming regular features of Canadian summers. With the tragic deaths from the 2021 BC heat dome still fresh in our memory, reliable ways to cool our homes are no longer optional—they’re essential.

That urgency is fueling government support for heat pump adoption. To cut emissions, improve efficiency, and protect people’s well-being, rebates are now available to help retrofit homes.

But here’s the catch: heat pumps only work as intended if they’re sized and installed properly. That takes two things: professional standards for accurate sizing, and honest conversations with homeowners about what their homes really need. This requires a fundamental shift by the industry from block load sizing to room-by-room calculations.

Let me quickly introduce myself.

I’m Todd Backus, COO of the Thermal Environment Comfort Association (TECA), a nonprofit trade association working to improve the HVAC industry through training, advocacy, and collaboration with regulators.

I’m a professional engineer with a Red Seal trade qualification in sheet metal. I’ve spent years designing and installing heat pumps and talking directly to homeowners about their comfort concerns. I’ve also seen firsthand the challenges contractors face. Those experiences led me to TECA, where I now focus on training professionals in proper system sizing and design—because I know the difference it makes when the job is done right.

What is the difference between room by room sizing and block load sizing?

• Block load sizing looks at the home as one whole unit, calculating heating and cooling needs for the house overall.
• Room by room sizing, on the other hand, breaks it down by each individual space.

This may not seem significant, but the difference in resulting design decisions can be huge. 

Block load tells you how big the system should be, but not where the heating and cooling needs to be delivered. Distribution systems, such as duct work or hydronic piping, are a common problem in new construction and retrofit projects when they are designed poorly.

For example, below-grade basements are naturally cooler. In the winter, they need a significant amount of heating to be comfortable, but in the summer, if you supply the same amount of cooled air, they will be far too cold. Room by room calculations reveal those issues and open the door to solutions — like installing a mini split system that allows you to heat or cool only the rooms that need it.

Existing HVAC systems can be difficult to modify, and some contractors may feel room by room isn’t worth the effort, especially if they don’t plan on upgrading ductwork. But I see it differently. Doing the calculation and sharing the report with homeowners gives them the information needed to make informed choices. It allows you to offer permanent solutions, especially in rooms that have persistent problems, such as adding a small secondary system to serve a space that has never been comfortable.

By providing homeowners with room-by-room reporting, it does two things:

1. It documents system deficiencies, which protects contractors from liability.
2. It gives the homeowner the choice. Maybe they’ll accept the limitations or maybe they’ll pay more to fix them. Either way, they’re making an informed decision—not discovering issues after the installation.

That transparency is huge for customer satisfaction, which should be a priority for all professionals in our industry.

Improper system sizing doesn’t just affect homeowners—it ripples through contractors, equipment suppliers, and the industry as a whole.

Problems for Homeowners

Many homeowners install heat pumps expecting lower costs, only to be disappointed when comfort and savings don’t materialize. 

Undersized systems struggle to maintain comfortable temperatures at peak conditions. Oversized heat pumps, especially in combination with undersized duct work, can lead to short cycling, which is inefficient and may cause the system to lock itself out to prevent damage. Insufficient airflow and short cycles will also impact the dehumidification process, further reducing thermal comfort.

Once the system is installed, it’s expensive to address these issues.

Problems for Contractors

Skipping room by room sizing may save time upfront, but it is a potential liability later. Heat loss and heat gain calculations are required by building code in Canada, the more thorough and accurate the calculation, the better the contractor will be protected if they have to justify their design decisions.

HVAC systems that aren’t designed for homeowner comfort will result in unhappy customers. Poor performance leads to complaints, bad reviews, and fewer jobs. As industry professionals, clients trust us to provide the expertise to lead them towards making good design decisions. 

If a contractor has failed to do their due diligence by not completing room by room calculations or examining the existing distribution system, in the event of a lawsuit, they could still be held responsible for damages, as ignorance and negligence are not valid legal defenses.

Problems for Equipment

Poorly sized distribution systems also impact the performance of the equipment. Oversized systems short cycle: the system turns on, satisfies the thermostat too quickly, then shuts off. You don’t get proper dehumidification or electrical efficiency because the equipment doesn’t work in the intended way. This can also happen if the thermostat is located too close to a supply air register.

There’s a common belief in the industry that newer heat pumps don’t really struggle with short cycling because of their improved turndown ratios. While it’s true that older units were often single speed, and today’s systems have turndown ratios that allow them to operate at partial loads, insufficient airflow from undersized ductwork and/or poor fitting selection is a persistent problem. Until we have systems that can truly modulate from zero to 100 percent, oversizing will continue to cause problems. 

Under sized equipment is less common but does still occur. In my experience, the under sizing typically takes place in the duct system, rather than the furnace or heat pump sizing. If the heat pump unit itself is undersized, at peak loads the client will not be able to maintain the desired temperature and may have to resort to portable units to attain the desired comfort levels.

Under sized ductwork can be extremely costly and challenging to modify later. Large sections are often hidden behind drywall, which is very disruptive for the client to remove and replace. On retrofits, consider what can be changed for the better beside the air handling unit. Often there are better fittings, filter locations, and duct sizing decisions that can be made to substantially improve system performance.

Problems for the Industry

Extreme weather events, such as the heat dome and the frequent wildfires, have forced us to re-evaluate our HVAC systems. They are no longer luxury items, they are health and safety equipment.

This fundamental change in our perspective must be reflected in the standards of our designs and installations. Demand for heat pump installation continues to rise, supported not only by the many incentives available, but also from clients who desire a higher standard of living, which includes thermal comfort.

At TECA, we see CSA F280 room by room calculations as essential for raising the bar on quality. HVAC design requires not only the correct sized equipment, but a properly designed distribution system as well. Poor system performance leads to frequent callbacks and cost disputes between the homeowners and HVAC professionals, which leave us all paying the price.  

As with many trades, the HVAC industry faces a skilled trade shortage. Canada has a significant task to train the next generation of trades professionals to keep pace with market demand. That’s where strong training, simple sizing tools, and clear requirements come in.

By making the room by room calculation the standard, and providing the tools for quick and reliable calculation, we can protect homeowners and professionals, and improve the industry as a whole.

The outcome? More reliable installations, faster growth for the industry and your business, and happier customers. And really, that’s what we should all be aiming for.